commit a75bf27fe41abe658c53276a0c486c4bf9adecfc upstream.
RETs in the lower half of cacheline may be affected by ITS bug, specifically when the RSB-underflows. Use ITS-safe return thunk for such RETs.
RETs that are not patched:
- RET in retpoline sequence does not need to be patched, because the sequence itself fills an RSB before RET. - RETs in .init section are not reachable after init. - RETs that are explicitly marked safe with ANNOTATE_UNRET_SAFE.
Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Reviewed-by: Josh Poimboeuf jpoimboe@kernel.org Reviewed-by: Alexandre Chartre alexandre.chartre@oracle.com Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com --- arch/x86/include/asm/alternative.h | 14 ++++++++++++++ arch/x86/include/asm/nospec-branch.h | 6 ++++++ arch/x86/kernel/alternative.c | 17 ++++++++++++++++- arch/x86/kernel/ftrace.c | 2 +- arch/x86/kernel/static_call.c | 2 +- arch/x86/kernel/vmlinux.lds.S | 2 ++ arch/x86/lib/retpoline.S | 13 ++++++++++++- arch/x86/net/bpf_jit_comp.c | 2 +- 8 files changed, 53 insertions(+), 5 deletions(-)
diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h index 0e777b27972b..d7f33c1e052b 100644 --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -80,6 +80,20 @@ extern void apply_returns(s32 *start, s32 *end);
struct module;
+#ifdef CONFIG_RETHUNK +extern bool cpu_wants_rethunk(void); +extern bool cpu_wants_rethunk_at(void *addr); +#else +static __always_inline bool cpu_wants_rethunk(void) +{ + return false; +} +static __always_inline bool cpu_wants_rethunk_at(void *addr) +{ + return false; +} +#endif + #ifdef CONFIG_SMP extern void alternatives_smp_module_add(struct module *mod, char *name, void *locks, void *locks_end, diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h index 4cc0ee529325..7ccaefaa16a6 100644 --- a/arch/x86/include/asm/nospec-branch.h +++ b/arch/x86/include/asm/nospec-branch.h @@ -226,6 +226,12 @@ extern void __x86_return_thunk(void); static inline void __x86_return_thunk(void) {} #endif
+#ifdef CONFIG_MITIGATION_ITS +extern void its_return_thunk(void); +#else +static inline void its_return_thunk(void) {} +#endif + extern void retbleed_return_thunk(void); extern void srso_return_thunk(void); extern void srso_alias_return_thunk(void); diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 3102e7cf6a48..ae4a6bc25b29 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -760,6 +760,21 @@ void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
#ifdef CONFIG_RETHUNK
+bool cpu_wants_rethunk(void) +{ + return cpu_feature_enabled(X86_FEATURE_RETHUNK); +} + +bool cpu_wants_rethunk_at(void *addr) +{ + if (!cpu_feature_enabled(X86_FEATURE_RETHUNK)) + return false; + if (x86_return_thunk != its_return_thunk) + return true; + + return !((unsigned long)addr & 0x20); +} + /* * Rewrite the compiler generated return thunk tail-calls. * @@ -776,7 +791,7 @@ static int patch_return(void *addr, struct insn *insn, u8 *bytes) int i = 0;
/* Patch the custom return thunks... */ - if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) { + if (cpu_wants_rethunk_at(addr)) { i = JMP32_INSN_SIZE; __text_gen_insn(bytes, JMP32_INSN_OPCODE, addr, x86_return_thunk, i); } else { diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c index 46447877b594..fba03ad16cce 100644 --- a/arch/x86/kernel/ftrace.c +++ b/arch/x86/kernel/ftrace.c @@ -367,7 +367,7 @@ create_trampoline(struct ftrace_ops *ops, unsigned int *tramp_size) goto fail;
ip = trampoline + size; - if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) + if (cpu_wants_rethunk_at(ip)) __text_gen_insn(ip, JMP32_INSN_OPCODE, ip, x86_return_thunk, JMP32_INSN_SIZE); else memcpy(ip, retq, sizeof(retq)); diff --git a/arch/x86/kernel/static_call.c b/arch/x86/kernel/static_call.c index 4544f124bbd4..42564d29eb1b 100644 --- a/arch/x86/kernel/static_call.c +++ b/arch/x86/kernel/static_call.c @@ -41,7 +41,7 @@ static void __ref __static_call_transform(void *insn, enum insn_type type, break;
case RET: - if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) + if (cpu_wants_rethunk_at(insn)) code = text_gen_insn(JMP32_INSN_OPCODE, insn, x86_return_thunk); else code = &retinsn; diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 6cee70927281..1f77896515c5 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -542,6 +542,8 @@ INIT_PER_CPU(irq_stack_backing_store); . = ASSERT(__x86_indirect_its_thunk_rax & 0x20, "__x86_indirect_thunk_rax not in second half of cacheline"); . = ASSERT(((__x86_indirect_its_thunk_rcx - __x86_indirect_its_thunk_rax) % 64) == 0, "Indirect thunks are not cacheline apart"); . = ASSERT(__x86_indirect_its_thunk_array == __x86_indirect_its_thunk_rax, "Gap in ITS thunk array"); + +. = ASSERT(its_return_thunk & 0x20, "its_return_thunk not in second half of cacheline"); #endif
#endif /* CONFIG_X86_32 */ diff --git a/arch/x86/lib/retpoline.S b/arch/x86/lib/retpoline.S index 9bde4e9d8c2a..01fcf0cd679b 100644 --- a/arch/x86/lib/retpoline.S +++ b/arch/x86/lib/retpoline.S @@ -281,7 +281,18 @@ SYM_CODE_START(__x86_indirect_its_thunk_array) .align 64, 0xcc SYM_CODE_END(__x86_indirect_its_thunk_array)
-#endif +.align 64, 0xcc +.skip 32, 0xcc +SYM_CODE_START(its_return_thunk) + UNWIND_HINT_FUNC + ANNOTATE_NOENDBR + ANNOTATE_UNRET_SAFE + ret + int3 +SYM_CODE_END(its_return_thunk) +EXPORT_SYMBOL(its_return_thunk) + +#endif /* CONFIG_MITIGATION_ITS */
SYM_CODE_START(__x86_return_thunk) UNWIND_HINT_FUNC diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 6225e8a8349f..c32270212640 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -408,7 +408,7 @@ static void emit_return(u8 **pprog, u8 *ip) u8 *prog = *pprog; int cnt = 0;
- if (cpu_feature_enabled(X86_FEATURE_RETHUNK)) { + if (cpu_wants_rethunk()) { emit_jump(&prog, x86_return_thunk, ip); } else { EMIT1(0xC3); /* ret */